[TenTec] Model 1220 frequency jump fix

[Carl Morris, WN3DUG]

Hello Bob, WB2VUF and the List,

While visiting Ten-Tec a while back, I mentioned the above problem and was
given a "Fix", which works for me on the 1220 and the 1230, 220 MHz Version,
as well.

Just add (Solder) an Electrolytic Capacitor, from about 1uF to 4.7 uF, 15VDC
or more, across Resistor  R32 (In parallel).  The Positive end of the
Capacitor goes toward the Base of Q8, the 2N4124 Transistor. This is the
side of R32 away from the Front Panel.

Evidently, when you let up on the PTT switch, the supply voltage jumps,
causing a power-on reset to the microprocessor.  The processor then retains
the old transmit frequency as the current receive frequency.  Ten-Tec
suggests several ways to try to correct this problem, including using
heavier wire from the power supply and shorter lengths, to prevent voltage
drops, and also adding a capacitor in the space labeled C86, on the PC
Board.  This capacitor should be an Electrolytic in the range of 1,000 to
4,700uF, rated at least 16VDC or more.  The Positive end should be oriented
as shown on the PC Board.  You may have to look around for a capacitor small
enough to fit on the space available on the board.  I had to use one with
both leads coming out the bottom, and adding a piece of wire and insulation,
to get a cap small enough to fit in the space.

I found that adding the capacitor across R32 is what cured the problem for
me. Adding C86 helped when the rig was used in mobile operation.